A process for the preparation of stannous chloride

Abstract

This invention relates to the field of chemical technology, specifically to a method for preparing stannous chloride. The method involves a redox reaction between metallic tin and selenium dioxide in a polar solvent under inert gas protection, producing stannous oxide and elemental selenium. Subsequently, without separating the intermediate products, hydrochloric acid is directly added to the same reaction vessel to chlorinate the stannous oxide, generating stannous chloride. The elemental selenium generated in situ acts as an endogenous reducing protectant, inhibiting the oxidation of divalent tin. This invention solves the problems of low purity and poor stability caused by the easy oxidation of stannous chloride during preparation in existing technologies, as well as the introduction of impurities through the addition of additional reducing protectants. This invention simplifies the production process through continuous oxidation, chlorination, and protection operations, avoiding the transfer and exposure of intermediate products. The in-situ dispersed elemental selenium preferentially reacts with oxidizing substances, significantly improving the chemical purity and stability of the obtained stannous chloride.

Description

Technical Field

[0001] This invention relates to the field of chemical processing technology, specifically a method for preparing stannous chloride. Background Technology

[0002] Stannous chloride, as an important chemical raw material and reagent, has wide applications in electroplating, catalysis and other fields. However, the mainstream preparation methods generally have the problem of controlling the stability of divalent tin in the product. The most conventional process is the direct reaction of metallic tin with hydrochloric acid. Although this method is simple, the stannous chloride generated is easily oxidized by dissolved oxygen in the solution or air encountered during the process in various stages such as reaction, concentration and crystallization, generating tetravalent tin impurities. This makes it difficult to improve the purity of the product, and the appearance is prone to yellowing. Moreover, its effective content as a reducing agent is unstable.

[0003] To address the oxidation problem, existing technologies often employ methods such as adding reducing metals like tin granules to the reaction system or introducing inert gas for protection. However, these methods have significant limitations. Physical inert gas protection cannot completely isolate trace amounts of oxygen, especially at the liquid-phase mass transfer interface, where oxidation can still occur. While adding excessive active metals for internal reduction has some effect, it introduces additional metal ion impurities, increasing the difficulty and cost of subsequent separation and purification, and complicating the process. Therefore, a preparation method that can highly suppress oxidation, is simple in process, and does not introduce exogenous impurities is needed. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing stannous chloride. Under the protection of an inert gas, metallic tin and selenium dioxide undergo a redox reaction in a polar solvent to generate stannous oxide and elemental selenium. Subsequently, without separating the intermediate products, hydrochloric acid is directly added to the same reaction system to chlorinate the stannous oxide and generate stannous chloride. The elemental selenium generated in situ in the reaction is used as an endogenous reducing protectant to inhibit the oxidation of divalent tin, thus solving the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing stannous chloride includes the following steps: S1. Oxidation reaction steps: Under the protection of an inert gas, metallic tin reacts with selenium dioxide in a polar solvent to produce a mixture containing stannous oxide and elemental selenium. S2, Chlorination and In-situ Protection Reaction Step: Without separating the elemental selenium generated in step S1, hydrochloric acid is directly added to the mixed system to react stannous oxide to generate stannous chloride, and the elemental selenium is used to inhibit the oxidation of stannous chloride. S3. Separation and purification steps: The reaction mixture obtained in step S2 is subjected to solid-liquid separation, and the liquid phase is concentrated and crystallized to obtain stannous chloride product.

[0006] Preferably, in step S1, the metallic tin is tin powder with a purity of not less than 99.9% and a particle size range of 150 mesh to 200 mesh.

[0007] Preferably, in step S1, the molar ratio of metallic tin to selenium dioxide is 1:1 to 1:1.05.

[0008] Preferably, in step S1, the polar solvent is anhydrous ethanol or deionized water, and the ratio of the volume (mL) of the added polar solvent to the mass (g) of metallic tin is 5:1 to 10:1.

[0009] Preferably, the reaction temperature in step S1 is 60℃-85℃, and the reaction time is 3h-6h.

[0010] Preferably, in step S2, the amount of hydrochloric acid added, based on the molar amount of hydrogen chloride it contains, is 2.2 to 3.0 times the molar amount of metallic tin added in step S1.

[0011] Preferably, in step S2, the temperature when adding hydrochloric acid is 70℃-90℃, and after the hydrochloric acid is added, the mixture is stirred and refluxed at 75℃-85℃ for 1h-2h.

[0012] Preferably, in step S3, the concentration is carried out in a water bath at 50℃-65℃ and under vacuum conditions below -0.08MPa, and the crystallization is carried out in a low-temperature environment at 0℃-5℃ for 12h-24h.

[0013] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention places the oxidation reaction of selenium dioxide on metallic tin and the chlorination reaction of hydrochloric acid in the same reaction environment and carries them out continuously. It also uses the elemental selenium produced in the first step reaction as an endogenous reducing protectant. This not only makes the reaction path seamless and the operation simpler, greatly simplifying the production process, but also avoids the separation, exposure and transfer of intermediate products from the source, thereby eliminating the drawbacks of oxidation risks and impurities introduced by multi-step operation.

[0014] 2. In this invention, selenium dioxide not only precisely oxidizes zero-valent tin to a divalent state, but the elemental selenium particles generated after its reduction also form a comprehensive reducing microenvironment during the subsequent chlorination reaction. This microenvironment can preferentially react with any invading oxidizing substances before divalent tin, thereby providing protection for unstable stannous chloride and significantly improving the chemical purity and stability of the product. Attached Figure Description

[0015] Figure 1 This is a flowchart of the preparation method of the present invention. Detailed Implementation

[0016] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] To address the issues of low product purity and poor stability caused by the easy oxidation of stannous chloride during the preparation process in existing technologies, and the potential introduction of impurities through the addition of additional reducing agents, please refer to [link to relevant documentation]. Figure 1 This embodiment provides the following technical solution: A method for preparing stannous chloride includes an oxidation reaction step, a chlorination and in-situ protection reaction step, and a product separation and purification step.

[0018] I. Oxidation Reaction Steps In a reaction vessel equipped with a stirrer, thermometer, reflux condenser and inert gas inlet and outlet pipes, an inert gas is continuously introduced to replace and maintain an oxygen-free environment for the reaction. The inert gas is preferably nitrogen or argon.

[0019] A polar solvent is injected into the reaction vessel as the reaction medium. The polar solvent is anhydrous ethanol or deionized water, and the ratio of the volume (mL) added to the mass (g) of metallic tin is 5:1 to 10:1.

[0020] Under continuous stirring and inert gas environment, metallic tin powder is added to a polar solvent. The purity of the metallic tin powder is not less than 99.9%, and the particle size range is 150-200 mesh.

[0021] After the tin powder is evenly dispersed, add selenium dioxide powder in batches while stirring to mix the tin powder and selenium dioxide. Control the molar ratio of tin to selenium dioxide to be between 1:1 and 1:1.05.

[0022] The purity of selenium dioxide is not less than 99.5%. Selenium dioxide can provide a gentler oxidation process and avoid the formation of tetravalent tin caused by the direct use of strong oxidants.

[0023] After the addition of materials is complete, the temperature of the reaction mixture is controlled between 60℃ and 85℃, and the reaction is continuously stirred at this temperature for 3-6 hours. During the mixing process, the tin powder and selenium dioxide undergo a redox reaction, and the reaction formula is as follows: 2Sn + SeO2 → 2SnO + Se↓ Once the metallic tin has completely reacted, a homogeneous suspension containing stannous oxide and elemental selenium is obtained.

[0024] II. Chlorination and In-situ Protection Reaction Steps After the reaction is complete, there is no need to filter and separate elemental selenium. Chlorination and in-situ protection are carried out directly in the same reaction vessel, and the stirring and inert gas protection are maintained during the reaction. At the same time, the temperature of the suspension in step one is adjusted to 70℃-90℃.

[0025] Concentrated hydrochloric acid with a mass concentration of 30%-36% is slowly added dropwise into the reaction environment using a constant-pressure dropping funnel. The total amount of concentrated hydrochloric acid added, based on the molar amount of hydrogen chloride it contains, is 2.2 to 3.0 times the initial molar amount of metallic tin. The dropping rate should be controlled to maintain a stable temperature rise in the reaction environment, and the entire dropping time should be controlled within 1-3 hours. Stannous oxide reacts with hydrochloric acid to produce stannous chloride and its byproducts. The reaction formula is as follows: SnO + 2HCl → SnCl₂ + H₂O During the dropwise addition process, the elemental selenium in the suspension preferentially combines with trace amounts of oxygen or any potential oxidizing substances that may be present in the reaction environment through its surface chemical adsorption and reactivity. This forms a continuous protective environment during the reaction, effectively inhibiting the oxidation of the generated stannous chloride to stannous tetrachloride. Furthermore, the selenium generated in situ can immediately exert its protective effect, which is more direct and uniform than adding selenium, resulting in better protection and higher product purity.

[0026] After the concentrated hydrochloric acid has been added, maintain the temperature of the reaction environment at 75℃-85℃, continue stirring and reflux for 1-2 hours to ensure that the chlorination reaction is complete.

[0027] III. Product Separation and Purification Steps After the reaction is complete, the reaction mixture is cooled to room temperature or below 30°C. Under the protection of an inert gas, the cooled reaction mixture is filtered under reduced pressure to achieve solid-liquid separation. The collected solid filter residue is mainly elemental selenium. It is washed 2-3 times with a dilute hydrochloric acid solution with a mass concentration of 5%-10%, and then washed 1-2 times with deionized water. The washed filter residue is dried to obtain elemental selenium as a byproduct.

[0028] All the filtrate and washing liquid collected during the separation process is an acidic solution of stannous chloride. The solution is transferred to a rotary evaporator and concentrated under reduced pressure at a water bath temperature of 50℃-65℃ and a vacuum condition below -0.08 MPa. Concentration is stopped when the solution volume is reduced to one-third of the original volume or when a thin film of crystals is observed to form on the vessel wall.

[0029] The concentrated solution was transferred to a crystallizer and allowed to stand for crystallization at a low temperature of 0℃-5℃ for 12-24 hours. After crystallization, wet crystals of stannous chloride dihydrate were obtained by filtration. To obtain an anhydrous product, the wet crystals were rapidly washed 1-2 times with a small amount of concentrated hydrochloric acid pre-cooled to 0℃-5℃. Finally, the washed crystals were placed in a vacuum drying oven and dried at a temperature of 60℃-80℃ and a vacuum condition below -0.09 MPa for 4-8 hours to obtain white or slightly gray anhydrous stannous chloride powder.

[0030] To illustrate the effects of this invention, the following examples and comparative examples will be used to provide a detailed explanation.

[0031] Example 1 In this embodiment, 200 ml of anhydrous ethanol was added to a 500 ml three-necked flask under argon protection, and the mixture was stirred. Then, 59.35 g of metallic tin powder and 55.50 g of selenium dioxide powder were added in sequence, with a molar ratio of tin to selenium of 1.00:1.00.

[0032] The temperature was raised to 75℃, and the reaction was carried out at this temperature with stirring for 4 hours to obtain a dark gray suspension. While maintaining stirring and an argon atmosphere, the temperature was adjusted to 80℃, and 220 mL of 36% concentrated hydrochloric acid was slowly added dropwise over 2 hours using a constant-pressure dropping funnel. After the addition was complete, the mixture was refluxed and stirred at 80℃ for 1.5 hours. After cooling, the reaction solution was filtered, and the selenium residue, after washing and drying, was weighed to be 46.8 g. The filtrate was concentrated under reduced pressure at 60℃ and -0.085 MPa to one-third of its original volume, and then placed in a 4℃ refrigerator for crystallization overnight.

[0033] The crystals obtained by vacuum filtration were washed with 20 mL of cold concentrated hydrochloric acid and then dried at 75 °C and -0.095 MPa vacuum for 6 h to obtain 145.2 g of white powdered anhydrous stannous chloride.

[0034] Chemical titration analysis showed that the product contained 99.4% SnCl2, 0.3% Sn(IV), and 8 ppm of selenium residue, with a product yield of 93% based on tin.

[0035] Example 2 The other conditions in this embodiment are the same as in Embodiment 1, except that the oxidation reaction conditions are changed.

[0036] The oxidation reaction temperature was reduced to 60°C, and the reaction time was extended to 6 hours. After the oxidation reaction, the chlorination and post-treatment steps were the same as in Example 1.

[0037] Finally, 142.7 g of anhydrous stannous chloride was obtained. The SnCl2 content in the product was 99.6%, the Sn(IV) content was 0.2%, the selenium residue was 6 ppm, and the product yield based on tin was 91.5%.

[0038] The results showed that a lower oxidation temperature combined with a longer oxidation time was beneficial to improving the chemoselectivity of the product and further reducing the Sn(IV) impurity content.

[0039] Example 3 In this embodiment, the reaction solvent was replaced with deionized water (250 mL). The oxidation reaction was carried out at 85°C for 3 hours.

[0040] Since water is the solvent, stannous chloride is more easily hydrolyzed. Therefore, after the chlorination stage, the reaction solution was cooled and a small amount of metallic tin particles were added and allowed to stand for 2 hours to reduce any trace amounts of Sn(IV) that may have been generated. The subsequent separation, concentration, crystallization, and washing steps were the same as in Example 1, but the filtrate was briefly treated with tin particles before concentration.

[0041] The final product yielded 140.5g, with a SnCl2 content of 99.0%, a Sn(IV) content of 0.7%, and a tin yield of 90%. This example demonstrates that the method of the present invention using water as a solvent is also feasible.

[0042] Comparative Example 1 This comparative example does not employ the integrated method of the present invention, but rather proceeds in steps. First, an oxidation reaction is carried out under the same conditions as in Example 1 to produce a mixture of stannous oxide and selenium. Then, instead of in-situ chlorination, the reaction solution is filtered to separate the solid, which is then washed with ethanol. This solid is resuspended in ethanol, and then concentrated hydrochloric acid is added dropwise under the same conditions for chlorination and post-treatment.

[0043] Final product analysis showed that the SnCl2 content was 97.8%, and the Sn(IV) content increased to 1.9%. This indicates that the separation step disrupted the close contact between selenium and stannous oxide, weakened the in-situ protective effect of selenium, and increased the probability of oxidation during subsequent processing and chlorination.

[0044] Comparative Example 2 This comparative example does not include selenium dioxide, thus avoiding the formation of in-situ protected selenium. Under argon protection, 59.35 g of metallic tin powder was directly suspended in 200 mL of anhydrous ethanol, and 220 mL of concentrated hydrochloric acid was added dropwise at 80 °C. After the reaction was complete, the same procedure was followed.

[0045] The resulting stannous chloride has a yellowish appearance, and analysis showed that the SnCl2 content was only 95.1%, while the Sn(IV) content was as high as 4.5%. This indicates that, without in-situ selenium protection, even under an inert atmosphere, the conventional reaction of tin with hydrochloric acid will still generate a relatively high proportion of tetravalent tin impurities, and the purity and stability of the product are not as good as those of the method proposed in this invention.

[0046] Working principle: Under an inert atmosphere, high-purity metallic tin powder and selenium dioxide undergo a redox reaction in a polar solvent. Selenium dioxide, as a mild oxidant, precisely oxidizes zero-valent tin to divalent stannous oxide, while simultaneously being reduced to elemental selenium. This avoids the over-oxidation problems that strong oxidants might cause, ensuring that the valence state of tin is precisely controlled at divalent. The generated stannous oxide exhibits high reactivity, while the simultaneously generated elemental selenium is highly dispersed in the entire reaction system as extremely fine particles.

[0047] Without any separation, concentrated hydrochloric acid is added directly to a suspension containing stannous oxide and elemental selenium. The hydrochloric acid reacts rapidly with the highly reactive stannous oxide to form stannous chloride. Simultaneously, the uniformly dispersed elemental selenium acts as an in-situ protectant. Its protective mechanism combines physical and chemical actions: thermodynamically, selenium's standard electrode potential allows it to react preferentially with any trace amounts of oxygen or other oxidizing agents present in the system, rather than divalent tin; kinetically, its large specific surface area allows it to rapidly adsorb and consume these oxidants. This is equivalent to creating a microscopic reducing barrier around each stannous chloride molecule being generated, effectively blocking its further oxidation to tetravalent tin.

[0048] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0049] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A method for preparing stannous chloride, characterized in that, Includes the following steps: S1. Under the protection of an inert gas, metallic tin powder and selenium dioxide are subjected to an oxidation-reduction reaction in a polar solvent to generate a suspension containing stannous oxide and elemental selenium. S2. Without separating the elemental selenium, concentrated hydrochloric acid is directly added to the same reaction system to chlorinate stannous oxide to generate stannous chloride, and the elemental selenium generated and dispersed in situ is used as an endogenous reducing protectant to inhibit the oxidation of the generated stannous chloride. S3. After the reaction is complete, the product is obtained by solid-liquid separation, filtrate concentration, crystallization and drying.

2. The method for preparing stannous chloride according to claim 1, characterized in that, For step S1, the purity of the tin powder is not less than 99.9%, and the particle size range is 150-200 mesh; the purity of the selenium dioxide is not less than 99.5%.

3. The method for preparing stannous chloride according to claim 1, characterized in that, For step S1, the molar ratio of metallic tin to selenium dioxide is 1:1 to 1:1.

05.

4. The method for preparing stannous chloride according to claim 1, characterized in that, For step S1, the polar solvent is anhydrous ethanol or deionized water; the ratio of the volume of the added polar solvent (in milliliters) to the mass of the tin powder (in grams) is 5:1-10:

1.

5. The method for preparing stannous chloride according to claim 1, characterized in that, For step S1, the temperature of the redox reaction is 60℃-85℃, and the reaction time is 3h-6h.

6. The method for preparing stannous chloride according to claim 1, characterized in that, For step S2, the mass concentration of concentrated hydrochloric acid is 30%-36%; the amount of concentrated hydrochloric acid added, based on the molar amount of hydrogen chloride it contains, is 2.2-3.0 times the molar amount of metallic tin initially added; the concentrated hydrochloric acid is added by dropping, with a dropping time of 1-3 hours, and the temperature of the suspension during dropping is 70℃-90℃.

7. The method for preparing stannous chloride according to claim 1, characterized in that, For step S2, after the concentrated hydrochloric acid is added, maintain the temperature of the reaction system at 75℃-85℃ and continue stirring and refluxing for 1-2 hours to ensure that the chlorination reaction is complete.

8. The method for preparing stannous chloride according to claim 1, characterized in that, For step S3, after the reaction is completed and cooled, solid-liquid separation is carried out under inert gas protection. The resulting solid filter residue is washed with dilute hydrochloric acid and deionized water, dried, and then recovered as elemental selenium by-product.

9. The method for preparing stannous chloride according to claim 1, characterized in that, For step S3, the concentration process is carried out in a water bath at 50℃-65℃ and under a vacuum of less than -0.08 MPa; the crystallization is carried out in a low temperature environment of 0℃-5℃ for 12h-24h.

10. The method for preparing stannous chloride according to claim 1, characterized in that, For step S3, the wet crystals obtained after crystallization are rinsed with concentrated hydrochloric acid at 0℃-5℃, and then dried at a temperature of 60℃-80℃ and a vacuum condition below -0.09 MPa for 4h-8h to obtain anhydrous stannous chloride powder.

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